One of the important preoccupations today in the field of polymers is to supply polymers of natural origin (biosourced) and/or that are biodegradable. For this purpose, it is interesting to be able to use biosourced monomers in the synthesis of the polymers.
The polyesters are mainly divided into two classes with different properties: the aliphatic polyesters, such as poly(butylene succinate) (PBS), poly(butylene succinate-co-adipate) (PBSA) or poly-ε-caprolactone (PCL), and the aromatic polyesters, such as poly(ethylene terephthalate) (PET), poly(trimethylene terephthalate) (PTT) or poly(butylene terephthalate) (PBT).
The aliphatic polyesters generally have melting points close to those of the polyolefins, which allows among other things their application in the fields of films and packaging, where biodegradability is obviously an advantage for single-use applications. However, they are very sensitive to hydrolysis. Some of the monomers used for synthesizing the aliphatic polyesters may be biosourced, for example succinic acid and 1,4-butanediol, used for synthesis of PBS. As for the aromatic polyesters, they have mechanical properties that are not readily compatible with the target applications of the polyolefins. Moreover, the high proportion of aromatic monomers in the composition of these polyesters greatly reduces the hydrophilicity of these resins and annihilates their biodegradable character.
To maintain mechanical properties close to those of the polyolefins while increasing the capacity of the aliphatic polyesters to resist hydrolysis, aliphatic-aromatic polyesters have been developed. This makes it possible to overcome some of the drawbacks of the purely aliphatic or purely aromatic polyesters.
From this perspective, PBAT (poly(butylene adipate-co-terephthalate)), marketed by BASF under the name Ecoflex®, was developed in order to meet the increasing need in Europe for biodegradable polymers, notably polymers intended for biodegradable packaging, making it possible to replace the polyolefins, at least in certain applications. PBAT also has excellent mechanical properties, notably in terms of elongation and of breaking stress.
Nevertheless, the amount of PBAT produced cannot at present meet all the needs of the market, which have been amplified by the legislation of certain European countries, which are increasingly requiring the use of biodegradable polymers in disposable packaging materials. Moreover, PBAT is petroleum-sourced at present, which has a considerable influence on its carbon footprint and therefore reduces the environmental benefit from using it in disposable packaging. Moreover, to achieve the improved mechanical properties and in particular the elongation properties, it is necessary to add relatively large amounts of terephthalic acid units.
Application WO 2009/135921 A1 describes biodegradable aliphatic-aromatic polyesters, in which the aromatic unit can be a furanoate unit. The polyesters described comprise a quantity of furanoate units, relative to the sum of the moles of units derived from diacids, well above 35 mol %. It is not described that this polyester can be formed by blow molding. Now, the applicant has ascertained that the polyesters described in that document, and notably the one in example 1, cannot be formed by blow molding as their crystallization rate is insufficient (see example 4.2 of the present document). Now, there is a need to obtain such polymers, as forming of polymers by blow molding, notably for forming polymer films of large dimensions, is an industrial necessity.
In this context, the applicant has demonstrated that it is possible to create other aliphatic-aromatic polyesters having properties close to, or even above, those of PBAT and formable by blow molding. These are in particular polyesters of poly(butylene succinate-co-furanoate) (PBSF) that comprise units derived from butanediol, from succinic acid and from 2,5-furandicarboxylic acid (FDCA), which may be of biosourced origin.
The mechanical properties of these polymers mean they can be used advantageously for manufacturing films and/or packaging.
Moreover, the applicant has devised a process for synthesis of these polymers which has, surprisingly, undeniable advantages over the processes described for the synthesis of other aliphatic-aromatic polyesters.